Laminated Touch Screen

ABSTRACT

In a touch screen having a flexible outer membrane with a first conducting surface, a backing surface with a second conductive surface, and sensors to detect contact between the first conducting surface and the second conducting surface, the improvement comprising the flexible outer membrane, wherein the flexible outer layer consists of an ultra-thin glass layer, a polymer layer; and an optical adhesive between the ultra-thin glass layer and the polymer layer, the optical adhesive holding the ultra-thin glass layer to the polymer layer.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. patent application Ser. No.12/050,008, filed Mar. 17, 2008, now U.S. Pat. No. 7,819,998 issued Oct.26, 2010, which is a Divisional of U.S. patent application Ser. No.10/603,518, filed Jun. 25, 2003, now U.S. Pat. No. 7,345,680 issued Mar.18, 2008, claiming priority of CA 2,391,745 filed Jun. 25, 2002, and areall incorporated by reference herein in their entirety.

Field of the Invention

The present invention relates to touch screen technology, and moreparticularly to resistive touch screen technology.

BACKGROUND TO THE INVENTION

Of various interfaces available for interacting with a computer systemone of the easiest to use and understand is the touch screen. Thistechnology allows a user to simply touch an icon or picture to navigatethrough the system, display the information the user is seeking, and toenter data. For this reason this technology is widely used in manyareas, including bank machines, information kiosks, restaurants, cars,etc.

A number of different methodologies are used to implement touch screentechnology, and each has advantages and disadvantages. The three maintypes of technology used are resistive, capacitive and surface acousticwave.

Resistive technology uses a flexible membrane that is affixed over adisplay. The membrane and display each have a conductive layer, andtypically the membrane is energized with an electrical potential. Whenthe membrane is touched, it is brought into contact with the conductivelayer on the display, and this creates current flow. Various sensorsaround the display measure the current and a controller can determine,either through an absolute value or through a ratio with the currentmeasured at other sensors, the location of the touch. One example ofthis technology is found in U.S. Pat. No. 4,220,815 to Gibson et al.

One of the advantages of resistive touch screens is that they can bepressed by either a finger or a stylus. The technology responds topressure and the pressure can be exerted by anything. This is importantin some cases where a user may wish to press the screen with the back ofa pen or other stylus, with fingernails or with gloved hands.

A second advantage is that they are sealed and not affected by dirt.Thus they can for example be used in industrial applications where theuser's hands may be greasy or dirty. Further, the touchscreen will workirrespective of whether there is dust or grime on the screen or in thearea around the periphery of the screen.

This technology will also continue to work even when scratches exist onthe outer surface of the membrane.

The main disadvantage of resistive touch screens to date has been thematerial from which the flexible membrane has been made. The requirementthat the membrane be flexible and resistant to breakage has generallymeant that polyester films have been used. The problem with these filmsis that they are easily scratched, torn and melted, and are thussusceptible to vandalism or inadvertent damage. This has generallylimited the use of this technology to applications where access to thescreens is restricted, and where the general public is not given accessto these machines. For example, information kiosks in shopping malls orairports do not typically use resistive touch screens due to thevandalism potential.

A second technology for touch screens is capacitive. In this technologya layer of glass is used as a dielectric, and typically has a sensorgrid on its lower surface. The touch of a user creates a change incapacitance that can be measured by the sensor grid, allowing thecontroller to determine when and where a touch occurs.

The advantage of capacitive touch screens is that their outer layer isglass, and thus more resistant to vandalism and damage.

One disadvantage of capacitive touch screens is that they can besusceptible to electromagnetic interference, and can thus produce falsehits. This interference can be caused by a number of things, but mostcommonly in public locations by cellular telephones and pagers. Due tothis potential interference, capacitive touch screen cannot be used incertain applications such as in some military equipment.

A second disadvantage is that the sensitivity of the screen can beaffected by dirt and scratches. These change the capacitance that issensed, and can create false touch signals.

Another disadvantage is that skin must be used to make contact with thedisplay. A stylus, fingernail or gloved hand will not produce a sensedtouch. Further, in some cases dry hands may not create a sensed touch.

A third technology that is used is the surface acoustic wave. In thistechnology ultra-sonic waves are emitted onto the surface of the screen,and microphones situated around the screen detect these waves. Theperiphery of the screen is generally reflective to the waves. When thescreen is touched the waves are affected, and a controller is able todetermine the location of the touch based on the information received bythe microphones.

The major problem with this technology is that it is susceptible to dustand dirt. Any particle will affect the waves. Further, when these typesof screens are cleaned, the dirt may be pushed to the periphery, whereit will affect the reflective surface. The result of the dirt is that atouch may be perceived to be in a different location than the actualtouch location.

What is therefore needed is a touchscreen technology that is robust, sothat it can sense the touch of a finger, gloved hand, or any stylus.Further, the technology is required to be unaffected by dirt andscratches. Also, the outer touch surface must be hard and resistant tovandalism.

SUMMARY OF THE INVENTION

The present invention overcomes the shortcomings of the prior art byproviding a glass laminate resistive touchscreen. This presents theadvantage of having the robustness of resistive touchscreen technologiesbut overcoming the difficulties of this technology by providing asurface that is resistant to scratching, cutting and burning, and thusis more difficult to vandalize.

The laminate of the present invention includes an ultra-thin layer ofglass to which a layer of polyester is adhered using an optical laminatematerial. The three layers are laminated to provide a uniformlytransparent yet flexible surface that is resistant to cracking andvirtually impossible to shatter.

One of the problems found with this laminate when used with touchscreens is that the different rates of thermal expansion of the variouslayers can cause rumples at the periphery of the polyester layer, whichcan cause false touch senses. The present invention also overcomes thisdifficulty by providing a mounting means that includes an elastictensioner such as silicon rubber to provide an elastic force ensuringthe polyester layer is always taut.

In a broad aspect, then, the present invention relates to a flexiblemembrane for a resistive touch screen display, said flexible membranecomprising: a glass laminate, wherein said glass laminate consists of:an ultra-thin glass layer; a polymer layer; and an optical adhesivebetween said ultra-thin glass layer and said polymer layer, said opticaladhesive holding said ultra-thin glass layer to said polymer layer.

In a further broad aspect, the present invention relates to a touchscreen having a flexible outer membrane with a first conducting surface,a backing surface with a second conductive surface, and sensors todetect contact between the first conducting surface and the secondconducting surface, the improvement comprising: the flexible outermembrane, wherein the flexible outer layer consists of an ultra-thinglass layer; a polymer layer; and an optical adhesive between saidultra-thin glass layer and said polymer layer, said optical adhesiveholding said ultra-thin glass layer to said polymer layer.

In another broad aspect, the present invention relates to a resistivetouch screen display, said display comprising: a flexible membrane,wherein said flexible membrane consists of: an ultra-thin glass layer; apolymer layer, said polymer layer being larger than said glass layer andsaid polymer layer extending beyond the periphery of said glass layer;and an optical adhesive between said ultra-thin glass layer and saidpolymer layer, said optical adhesive holding said ultra-thin glass layerto said polymer layer; a backing surface; a pressure sensitive adhesiveaffixed between the periphery of said polyester layer and said backingsurface; an elastic tensioner affixed between the periphery of saidpolyester layer and said backing surface, said elastic tensioner beingadjacent to said pressure sensitive adhesive; a first conductive layeraffixed to said polyester layer; a second conductive layer affixed tosaid backing surface; and sensors used to detect where said firstconductive layer contacts said second conductive layer.

In yet another broad aspect, the present invention relates to a processfor the creation of a flexible laminate membrane for a resistive touchscreen, the flexible laminate membrane having a glass layer and apolyester layer, the process comprising the steps of: applying anoptical adhesive to said glass layer; affixing a polyester layer oversaid optical adhesive; rolling said optical polyester layer from thecenter of said polyester layer outwards to remove excess opticaladhesive and air bubbles; and pressing said polyester layer, glass layerand optical adhesive combination in a high pressure press to ensure auniform level of optical adhesive.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the nature and objects of theinvention, reference should be had to the following detailed descriptiontaken in connection with the accompanying drawing in which:

FIG. 1 shows a side elevational cross-sectional view of theglass-polyester laminate of the present invention;

FIG. 2 shows a side elevational cross-sectional view of a one touchscreen assembly using the laminate of FIG. 1, in which a false touch ispresent;

FIG. 3 shows a side elevational cross-sectional view of one solution tothe false touch problem of FIG. 2; and

FIG. 4 shows a side elevational cross-sectional view of a preferredembodiment of the touch screen assembly of the present invention whichovercomes the false touch problem of FIG. 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

As discussed above, resistive touch screen technology would be thepreferred technology for numerous applications, especially those inwhich the public needed to use touch screens. The robustness of thistechnology allows it to function regardless of dirt, dust, orelectromagnetic signals. The screen can be touched by a bare hand,gloved hand, or stylus and still function. However, the main problemthat needs to be overcome is the vulnerability of the soft uppertouchscreen layer.

It has been found by the inventor that a thin glass layer possessesenough flexibility to allow it to be used for touch screen applications.Glass useful for this purpose includes Schott Borofloat D263™ or Corning0211™ and is generally about 0.5 mm thick although greater or lesserthicknesses are possible as long as the glass behaves like a film.Further, by having an outer glass layer, the problems of a soft polymerouter layer are overcome. Glass is much harder, and thus not susceptibleto being cut or burned. It is also more resistant to scratches andgeneral wear and thus its use increases the life of touch screens.

The problem with ultra-thin glass however is that it is very brittle,and easily cracks and shatters with very minimal contact. Glass hastherefore not been used previously for resistive touch screens.

Reference is now made to FIG. 1. The inventor has found that theaddition of a polymer substrate layer 30 laminated to the ultra-thinglass layer 20 using an optical adhesive 40 overcomes the brittleness ofthe glass. The creation of this laminate 10 makes it extremely difficultto crack glass layer 20, and glass layer 20 can be bent and pressedwithout risk of breakage. Further, even if cracking does occur, polymersubstrate 30 ensures that glass layer 20 does not shatter, and resistivetouch screen laminate 10 remains intact and functional.

In a preferred embodiment, polymer layer 30 of laminate 10 is apolyester, and will be referred to hereinafter as polyester layer 30.One skilled in the art will however appreciate that other suitablepolymers can be used. Polyester layer 30, in the preferred embodiment,comprises a polyester film, also referred to in the art as PET, with athickness of approximately 0.007 inches, or 0.175 mm. Suitable filmsinclude ICI Melnex™ or Dupont Clear Mylar™. However, the use of otherfilms is contemplated, and in one embodiment it is envisioned thatpolyester layer 30 may even be opaque to provide a fixed graphic for thetouch screen.

In one embodiment of the invention, a conductive silver buss bar (notshown) may be used to help the transmission of current flow frompolyester layer 30. Such conductive layers are well known in the art andare typically applied using a silk screen process. However, it is alsocontemplated that no buss bar be used in an alternative embodiment, inwhich polyester layer 30 is used without such a bar.

Polyester layer 30 and ultra-thin glass layer 20 are laminated togetherusing a liquid or film optical adhesive 40. One skilled in the art willrealize that optical adhesive 40 forms a thin layer between polyesterlayer 30 and glass layer 20, and that FIGS. 1 to 4 show an exaggeratedthickness for this layer for illustrative purposes only.

Optical adhesive 40 is transparent and provides sufficient durability tohold the two layers 20 and 30 together. One suitable optical adhesivehas been found to be Norland™ Optical Adhesive 61. The skilled personwill however realize that other suitable adhesives may be used.

In applying adhesive 40, it is aesthetically preferable to ensure thatthe adhesive is applied evenly and with no bubbles or gaps, creating alaminate 10 that is uniformly planar and transparent. This laminationprocess involves applying a relatively thick layer of optical gluebetween glass layer 20 and polyester layer 30. The layer of glue must bethick enough to allow air bubbles to be squeezed out, which is much moredifficult to do when thin layers of glue are applied.

In practice, layers 20 and 30 are laminated together with glue, and aroller is used to squeeze out excess glue and air bubbles. The roller ispreferably applied from the centre of laminate 10 and rolls towards theedges of the laminate. A wave of glue and air bubbles is thus propelledto the edges of laminate 10, leaving a thin layer of glue with fewer orideally no air bubble behind.

After rolling, laminate 10 is placed between a pair of ¼″ (0.64 cm)thick steel plates, and the plates are actuated by a press to apply 5-10tonnes of pressure to the laminate. More or less pressure may be appliedas required. The primary purpose of the pressure is to evenly distributethe glue between glass layer 20 and polyester layer 30 to eliminate highand low spots.

During the application of pressure, an absorbent medium such as tissueis placed between the laminate and the steel plates to protect thelaminate and absorb the excess glue that is squeezed out. At the end ofthe lamination process, the thickness of the glue is preferably limitedto 0.001-0.002 inches (0.025-0.05 mm).

Reference is now made to FIG. 2. Laminate 10 is typically made withlower polyester layer 30 being larger than upper glass layer 20. Bycreating a larger lower surface the laminate is easier to make.

Optical adhesive 40 also preferably extends beyond the edges of glasslayer 20 and is allowed to build up slightly about the edges of glasslayer 20. This locks glass layer 20 in place and makes it harder to moveor separate from polymer layer 30. The buildup of optical adhesive 40also prevents microfractures in the glass caused by cutting frompropagating into larger fractures.

Experimenting with the laminate, the inventor has found that a problemcan arise due to the different thermal expansion rates of lowerpolyester layer 30, adhesive 40 and upper glass layer 20. Polyesterlayer 30 and adhesive 40 have similar expansion rates, but glass layer20 and polyester layer 30 have very different expansion rates, polyesterlayer 30 having a higher expansion rate than glass layer 20.

When applied to a touch screen display 50 these expansion rates cancreate false touches or shorts 35 between touch screen laminate 10 andthe backing display layer 70. This happens when touch screen display 50is exposed to different temperature extremes. When it is cold, polyesterlayer 30 will shrink.

Touch screen membranes are typically mounted to a backing surface 70using a pressure sensitive adhesive 60 along the periphery of the outertouch screen layer. This adhesive 60 has a bubble-gum like texture andis not elastic.

When polyester layer 30 shrinks when exposed to cold, pressure sensitiveadhesive 60 stretches to allow the polyester layer 30 to contract. Thetouch screen display 50 will still function at this point. However, whentouch screen display 50 is warmed up again, polyester layer 30 willexpand, and since pressure sensitive adhesive 60 is not elastic, thepolyester will tend to rumple between pressure sensitive adhesive 60 andspacer dots 80 used to maintain a normal spacing between the conductivecoating applied to the lower edge of layer 30 and the upper surface ofbacking surface 70, as illustrated by false short 35. While notillustrated, one skilled in the art will realize that spacer dots 80 canbe affixed to either polyester layer 30 or backing surface 70.

Glass layer 20 tends to keep the remainder of polyester layer 30 flat,and thus the expansion will be reflected completely or at leastprimarily along the edge of glass layer 20. In the prior art, thecompletely polymer touch screen would distribute this expansion evenly.However, due to adhesive 40 and glass layer 20, this does not occur inlaminate 10, and the problem of false touches is increased in thosecases in which the screens are exposed to temperature extremes.

Reference is now made to FIG. 3. One possible solution to the aboveproblem is to expand glass layer 20 to the edges of polyester layer 30.This would ensure that polyester layer 30 remains flat against glasslayer 20, to limit or prevent false touches.

A possible problem with this solution is that adhesive 40 may fail dueto repeated expansion or contraction of polyester layer 30 without theouter expansion area shown in FIG. 2. In the solution of FIG. 3,adhesive layer 40 absorbs all of the stress induced by the differingexpansion rates of the glass and polyester. Eventually it is envisionedthat optical adhesive 40 could fail and separation of glass layer 20 andpolyester layer 30 could occur.

A preferred solution to the above problem is illustrated in FIG. 4. Inthis embodiment, a polyester layer 30 is larger than glass layer 20,thus still permitting ease of manufacture. It also allows opticaladhesive 40 to be built up about the edges of glass layer 20 to betterhold glass layer 20 to polyester layer 30.

In order to overcome the false touch problem, an elastic tensioner 110is added to touch screen display 50 to circumscribe adhesive 60.Further, an active area insulator 120 is added between polyester layer30 and elastic tensioner 110.

Elastic tensioner 110 preferably comprises silicon rubber. In operation,elastic tensioner 110 creates an elastic force that normally biases orstretches polyester layer 30 outwards. Therefore, if display 50 becomesvery cold, polyester layer 50 will shrink, pulling pressure sensitiveadhesive 60 inwards, along with elastic tensioner 110. When the display50 is later warmed, elastic tensioner 110 pulls polyester layer 30 backto its original configuration, reducing the possibility of rumples, andthus false touches.

Area insulator 120 further aids in preventing a false short 35 byproviding a non-conductive layer in the area most likely to make falsecontact. Area insulator 120 comprises an ultraviolet ink film printedonto the lower surface of the polyester layer 30 along its outer edges.As one skilled in the art will appreciate, the thickness of areainsulator 120 in FIG. 4 has been exaggerated for illustrative purposed,and in practice area insulator 120 adds no significant spacing betweenpolyester layer and backing surface 70.

Area insulator 120 reduces the chances of electrical contact betweenpolyester layer 30 and display layer 70. It has been found that pressuresensitive adhesive 60 is insufficient for this purpose.

Area insulator 120 bonds aggressively, perhaps covalently, to polyesterlayer 30, and thus pressure sensitive adhesive 60 and elastic tensioner110 are essentially bonded to polyester layer 30 itself.

One skilled in the art will realize that the emdiments illustrated inFIGS. 2 and 3 will typically also have an area insulator layer 120between polyester layer 30 and pressure sensitive adhesive 60.

When combined, the above configuration provides a resistive touch screenwith an outer glass layer, overcoming the difficulties of the prior art.The above configuration further provides a means to compensate for thedifferent thermal expansion rates of the different materials of thelaminate.

Although the present invention has been described in detail with regardto the preferred embodiment thereof, one skilled in the art will easilyrealize that other versions are possible, and that the invention is onlyintended to be limited in scope by the following claims.

1-35. (canceled)
 36. A flexible membrane for a resistive touch screendisplay, said flexible membrane comprising: a glass laminate, whereinsaid glass laminate comprises: an ultra-thin glass layer and a polymerlayer having upper and lower surfaces; an optical adhesive between saidultra-thin glass layer and said upper surface of said polymer layer,said optical adhesive holding said ultra-thin glass layer to saidpolymer layer.
 37. The membrane of claim 36, said polymer layer beinglarger than said glass layer to extend beyond the periphery of saidglass layer.
 38. The membrane of claim 37, wherein said optical adhesiveis allowed to build-up about said periphery of said glass layer.
 39. Themembrane of claim 36, wherein said glass layer is approximately 0.5 mmthick.
 40. The membrane of claim 39, wherein said polymer layer is apolyester film approximately 0.175 mm thick.
 41. The membrane of claim40, wherein said optical adhesive is formed in a uniform thickness inthe range of 0.025 and 0.05 mm between said glass layer and said polymerlayer.
 42. The membrane of claim 36 comprising an insulating filmapplied in a peripheral band to said lower surface of said polymerlayer.
 43. The membrane of claim 42 wherein said insulating film isultraviolet ink.
 44. In a touch screen having a flexible outer membranewith a first conductive surface, a backing surface with a secondconductive surface, and sensors to detect contact between the firstconductive surface and the second conductive surface, the improvementcomprising: the flexible outer membrane, wherein said flexible outermembrane comprises: an ultra-thin glass layer; a polymer layer havingupper and lower surfaces; and an optical adhesive between saidultra-thin glass layer and said upper surface of said polymer layer,said optical adhesive holding said ultra-thin glass layer to saidpolymer layer.
 45. The touch screen of claim 44, said polymer layerbeing larger than said glass layer to extend beyond the periphery ofsaid glass layer.
 46. The touch screen of claim 45, wherein said opticaladhesive is allowed to build-up about said periphery of said glasslayer.
 47. The touch screen of claim 44, wherein said glass layer isapproximately 0.5 mm thick.
 48. The touch screen of claim 47, whereinsaid polymer layer is a polyester film approximately 0.175 mm thick. 49.The touch screen of claim 48, wherein said optical adhesive is formed ina uniform thickness in the range of 0.025 and 0.05 mm between said glasslayer and said polymer layer.
 50. The touch screen of claim 44comprising an insulating film applied in a peripheral band to said lowersurface of said polymer layer.
 51. The touch screen of claim 50 whereinsaid insulating film is ultraviolet ink.
 52. A resistive touch screendisplay, said display comprising: a backing surface; a pressuresensitive adhesive affixed between the periphery of a polymer layer andsaid backing surface; an elastic tensioner affixed between the peripheryof said polymer layer and said backing surface, said elastic tensionerbeing adjacent to said pressure sensitive adhesive; a first conductivelayer applied to said lower surface of said polymer layer; a secondconductive layer applied to said backing surface; sensors used to detectwhere said first conductive layer contacts said second conductive layer;and a flexible membrane, wherein said flexible membrane comprises: anultra-thin glass layer; said polymer layer, said polymer layer beinglarger than said glass layer to extend beyond the peripheral edges ofsaid glass layer by a predetermined distance in each direction; and anoptical adhesive between said ultra-thin class layer and said polymerlayer, said optical adhesive holding said ultra-thin glass layer to saidpolymer layer.
 53. The touch screen of claim 52, wherein said opticaladhesive is allowed to build-up against said peripheral edges of saidglass layer.
 54. The touch screen of claim 52, wherein said glass layeris approximately 0.5 mm thick.
 55. The touch screen of claim 54, whereinsaid polymer layer is a polyester film approximately 0.175 mm thick. 56.The touch screen of claim 55, wherein said optical adhesive is formed ina uniform thickness in the range of 0.025 and 0.05 mm between said glasslayer and said polymer layer.
 57. The touch screen of claim 52, whereinsaid ultraviolet ink film is applied in a band to extend inwardly, bypredetermined amount, onto said lower surface of said polymer layerrelative to said pressure sensitive adhesive to provide a zone ofinsulation between said lower surface of said polymer layer and saidbacking surface inwardly adjacent of said pressure sensitive adhesive.58. The touch screen of claim 52 additionally comprising an areainsulator layer between said polymer layer and said pressure sensitiveadhesive.
 59. The touch screen of claim 58 wherein said area insulatorlayer comprises an ultraviolet ink film.